Fix two problems in the spi subsystem:

1) spi subsystem core dumps when modular spi master is unloaded.
2) spi subsystem core dumps when spi slave device is suspended/resumed and
   module slave driver is not loaded.
Signed-off-by: Stephen Street <stephen@streetfiresound.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>